Chemical and biological oceanographic surveys of the Gulf of Papua and Torres Strait (1979)

Brief description

An oceanographic survey of the Gulf of Papua and Torres Strait was undertaken in November and early December 1979, prior to the monsoon season. In the Gulf of Papua, sampling positions were selected to measure the diffusion of river water into the Gulf. An additional transect was made through the Great Barrier Reef Lagoon (from the Coral Sea to slightly west of Torres Strait) in a preliminary examination of zooplankton production. This dataset contains temperature, salinity, dissolved oxygen, dissolved inorganic and organic nutrient, chlorophyll and phaeophytin data from a range of depths at the 45 stations sampled during this survey. Zooplankton abundance data is also available for 12 stations.Comparisons of AIMS and CSIRO sampling and analytical methods were also made at an intercalibration station in the Coral Sea off Raine Entrance. The Gulf of Papua is bordered by a coastline of very high productivity with extensive mangrove forests, and is the catchment area for massive freshwater runoff from the Fly, Turama, Aird and Purari River systems. The adjoining Torres Strait forms a potential pathway for transport of waters between the Arafura Sea and the Coral Sea. The effects of water circulation in this region on the reef ecosystems is of considerable scientific interest. A number of additional studies of currents and water movements were also undertaken simultaneously with this cruise, within these waters and the northern region of the Great Barrier Reef. Measurements of the discharge of streams flowing into the Gulf of Papua were programmed by the Office of Minerals and Energy of Papua New Guinea. A CSIRO buoy was also released from RV Lady Basten in the Gulf of Papua during this period and tracked by satellite. The Coastal Zone Colour Scanner on board NOAA satellite Nimbus-7 was programmed for operation over the northern Great Barrier Reef during the cruise. Moored current meters and water level recorders were also deployed by AIMS for several weeks in this period at various locations in the northern region of the Great Barrier Reef. Towards the conclusion of this cruise, geophysical tows were made by the Australian Department of Mineral Resources in the Great Barrier Reef lagoon, south of 11°S. The AIMS components of these additional studies are described separately.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Statement: 1. Water sampling and temperature:Water samples were collected with 5 litre Niskin bottles (General Oceanics) fitted with reversing thermometers ( Rigosha) to obtain simultaneous temperature measurements. The Niskin bottles were deployed to particular depths estimated by the length of wire paid out, after which a period of 10 minutes was left before closing to allow temperature equilibration and flushing of water within the bottles. On board, a further 20 minutes was left before reading the temperatures to allow the thermometers to stabilize with the laboratory temperature. Temperatures were read to ± 0.05°C. 2. Dissolved Oxygen:Samples for dissolved oxygen analysis were routinely taken first from the Niskin bottle. Seawater was slowly drawn into a 300ml glass stoppered BOD bottle via plastic tubing from the bottom tap of the Niskin bottle. A volume of approximately 500ml was allowed to overflow and flush out seawater which had been in contact with air. Manganous sulphate and alkaline iodide reagents were immediately added, the bottle shaken vigorously until the precipitate was evenly dispersed and then stored underwater until analysis within 6 hours. Dissolved oxygen was determined by the Winkler method as described in Strickland, J.D.H. and T.R. Parsons, 1972. A practical handbook of seawater analysis. Bull. Fish. Res. Bd. Canada, 167: 1-310.3. Salinity:Water samples for salinity determinations were taken into 500ml polyethylene bottles, which had been rinsed twice with the sample water, and tightly closed with sealing screw caps. The samples were analyzed on board within two days. Salinity was measured with a Plessey, Model 623CN Laboratory salinometer, standardized with IAPSO standard seawater. The measurement was accurate to ±0.003ppt.4. Nutrients:Nutrients analysed in this sampling program included ammonia, nitrate, nitrite, phosphate and silicate. Samples for ammonia were drawn directly into sample bottles without filtration, since the filtration process was shown to contaminate these samples. For the remaining nutrients, sample water was filtered through a 0.45 µm Millepore filter at a vacuum pressure not exceeding 180 mm Hg. All sample bottles (plastic, 100 ml capacity) for nutrients had been previously HCl acid washed, and were rinsed 3 times with a small amount of the sample water before filling. Most samples were analysed on board within 2 hours of collection, using a multichannel autoanalyser system developed at this institute for low nutrient levels in seawater (see Ryle, V.D., H.R. Mueller and P. Gentien, 1981. Automated analysis of nutrients in tropical sea waters. AIMS Tech. Bull., Oceanography Series No.3).Samples which could not be analysed immediately were preserved with 0.6% chloroform following the recommendation of Gilmartin (1967) for phosphate, and stored in a deep freezer for up to one month before analysis. (see Gilmartin, M., 1967. Changes in inorganic phosphate concentration occurring during seawater sample storage. Limnol. and Oceanogr. 12: 325-328.). Such storage has proven quite satisfactory. The detection limits for these nutrients with our techniques are ammonium (0.2 ug at/l), nitrate(0.05 ug at/l), nitrite (0.02 ug at/l), phosphate (0.02 ug at/l) and silicate (0.4 ug at/l).Dissolved organic nitrogen (DON) and phosphate (DOP) were determined by the ultra-violet photo-oxidation method with a Photooxidation unit (La Jolla Scientific Co., Model PO-14). These determinations were made on samples which had been stored frozen for up to one month, using the same Autoanalyzer system above. The organic fractions of total nitrogen and phosphate were calculated as the difference in concentrations before and after oxidation.5. Phytoplankton pigments:Samples of 500 ml were filtered onto 47 mm diameter GF/C glass fibre filters at a vacuum pressure not exceeding 180 mm Hg. Approximately 1ml of 1% Mg CO3 solution was added to the samples during filtration to stabilize the pigments in the extraction process. The filters were folded in half, placed in black plastic containers and frozen until analysis, mostly within two weeks of collection. Chlorophyll a and phaeo-pigments were analysed by the fluorometric method of Strickland and Parsons (1972), using a Turner Model 111 fluorometer. (See Strickland, J.D.H. and T.R. Parsons, 1972. A practical handbook of seawater analysis. Bull. Fish. Res. Bd. Canada, 167: 1-310).6. Microplankton:A 4 litre sample was taken into a wide mouth plastic container and preserved with formalin (buffered with sodium tetraborate) to a final concentration of 1%. In the laboratory, the microzooplankton were concentrated for counting by the following procedures recommended by Dr A. Taniguchi, Tohoku University, Japan (personal communication).The samples were allowed to stand without disturbance for at least 24 hours. Following this, the supernatant seawater was slowly siphoned off with glass tubing, leaving the settled organisms on the bottom of the container in about 500 ml of water. This volume was rinsed into a 500 ml measuring cylinder, again allowed to settle over 24 hours, and siphoned off to leave about 50 ml. The procedure was repeated with a smaller measuring cylinder which finally concentrated the sample down to 12 ml. About 2 ml of this volume was allowed to evaporate to increase salinity and prevent fungal growth.A subsample of 1 ml was taken from the mixed contents of this concentrated sample and counted on a Zeiss plate chamber with a Nikon inverted microscope (Model MS). The animals were identified to Class or lower taxonomic level. 7. Net zooplankton:Zooplankton samples were collected with a conical net of 205 um mesh, the dimensions of which were 0.45 m diameter and 1.5 m length. The actual water volume passing through the net was estimated by a flow meter (Rigosha) mounted on the mouth ring. The net was towed by a winch vertically from the bottom to the surface at a constant speed of 1 m/s. The samples were preserved with buffered formalin (sodium tetraborate) to 10% concentration for biomass measurement and counting. Biomass was measured in the following way before counting. The sample was decanted first into a wide petri dish from which large animals, such as medusae, fish larvae and salps were removed. The sample was then gently filtered onto a 60 um preweighed mesh disc and rinsed with filtered sea water. The mesh disc containing the zooplankton was very gently blotted onto Whatman No. 1 filter paper until no further moisture was observed to come through. The sample was then immediately weighed on a Sartorius 1205 MP top-pan balance with a sensitivity of 0.005 g. After weighing, the zooplankton sample was returned to fresh 10% buffered formalin-sea water solution. Dried zooplankton material was calculated to be 15.2% (± 0.9, n = 41) of the "wet" biomass as measured above.Zooplankton was counted using Bogorov trays under a dissecting microscope. Initially, all of the large and rare animals were removed and counted separately. Counts of other animals were made on a subsample containing between 500 and 1500 animals, usually a split of the original sample of 1 in 16. Zooplankton were mostly identified to Class taxonomic level and to the level of Order with crustaceans. The category "Others" includes radiolarians, ciliates and platyhelminthes.8. IntercalibrationOn the 5 December, 1979, an intercalibration station in the Coral sea off Raine Entrance was sampled by scientists on RV Lady Basten (AIMS) and RV Sprightly (CSIRO) to compare sampling methods and analytical procedures. Water samples were taken simultaneously from the two vessels standing within 0.5 km and subsamples for oxygen, nutrients and salinity were exchanged between members of the two research institutions.

Notes

Credit
Wolanski, Eric J, Dr (Principal Investigator)